As it is known, transport chains of the type specified above have to satisfy the need to carry out paths which are not only straight but that also include more or less pronounced curves.
Many of the transport chains currently used have the disadvantage that, when in a curve, and in particular at the extrados, open spaces are formed between adjacent links, which spaces not only interrupt the continuity of the support surface, but may also cause failures or accidents, when at the end of the curve such spaces should close onto a foreign object, a transported article, or on a finger of an operator, which have meanwhile occupied these open spaces.
The presence of such open spaces can also cause falling of the transported articles from the transport chain when the articles undergo accelerations or decelerations to adapt their speed to that of the chain. This can happen for example when the items are transferred from a transport chain that is moving at a first speed to a transport chain that is moving at a second speed different from the first.
For this reason transport chains have been proposed that comprise links carrying plates having an arched profile, which plates are able to engage in corresponding arched seats on the links themselves. In this way, when in a curve, no open space is formed, since the arcuate plate of each link is capable of articulating in the corresponding arcuate seat.
An example of a transport chain of this type, also called in jargon “zero-gap”, is shown in European patent application EP 926082. In particular, each link of the transport chain includes a support surface having an arcuate seat and a pin having a plate-like head with an arcuate profile: the plate-like head is at the same level of the support surface and extends along the link up to engage the corresponding curved seat.
However, such a transport chain, while being able to avoid the formation of open spaces in the support surface when in a curve, does not appear to be advantageous in other respects. In fact, in a transport chain of this type, the longitudinal dimensions—that is, along the sliding direction of the chain—of each link must be necessarily high, as the support surface of each link must be large enough for housing the plate-like head of the corresponding pin. Since the longitudinal dimensions of the links are closely related to the minimum pitch obtainable between adjacent links of the transport chain, a transport chain of the type described in European patent application EP 926082 has a relatively large pitch.
A transport chain similar to the above is also described in European patent EP 910540.
Another example of a zero-gap transport chain is provided in European patent application EP 1375391, in which the pin associated with a link of the chain is connected to a plate-like portion having an arcuate profile provided with a rear extension adapted to act as a support surface connecting the plate-like portion itself and the support surface provided by the previous link.
A still further example of the zero-gap transport chain is shown in European Patent EP 2349877.
The fact of not being able to have a reduced pitch is a drawback of the transport chain in all those applications. In particular, the minimum radius of curvature of the path the links of the chain are able to travel is determined by the pitch between the links themselves. If the pitch between the links is relatively high, the transport chain will only be possible with curves having a relatively large radius of curvature.
Accordingly, the problem that underlies the present invention is to devise a transport chain capable of offering as support surface which does not exhibit open spaces between the links when in a curve, and at the same time exhibits structural and functional features to alleviate said drawback of the zero-gap transport chains known in the state of the art.